Analysen zur Interaktion von Meeresspiegelanstieg, Sturmfluten und Morphologie im nordfriesischen Wattenmeer

Coastal protection measures in Germany are designed, dimensioned and built in accordance with the applicable requirements for safe and sustainable storm surge protection. However, a major challenge is to estimate the design parameters required in the future, in particular due to the influence of sea level changes and the associated changes in hydrodynamic and morphodynamic processes. The present article aims at evolving the scientific-technical foundation for sustainable coastal protection structures at the North Sea and Baltic Sea coasts by a combination of numerical as well as statistical analyses.

The state of the art for the estimation of the effect of sea level rise on future design water levels are hydrodynamic-numerical models. The consideration of morphodynamics in those is often neglected due to lack of data and limited computational capacities. In order to estimate the influence of morphodynamics, a hydro-morphodynamic model of the North Frisian Wadden Sea was evaluated in the present analyses. On the one hand, the influence of the bathymetry (static, annual-variable and morphodynamic) on the resulting water level simulations was quantified, and on the other hand, we investigated whether the rise of mean sea level on extreme water levels can be compensated by taking morphodynamics into account.

Based on the performed model configurations it could be shown that the consideration of bathymetric changes within a hydrodynamic-numerical model has a significant influence on the trends and variability of water levels in the North Frisian Wadden Sea. Furthermore, the subsequent extreme value analyses of the scenario runs on mean sea level rise partly suggest that in individual tidal basins morphodynamics, i.e. the increase or decrease of tidal flat areas, is able to mitigate the influence of sea level rise on extreme water levels (return intervals > 100 years). Also, the influence on extreme water levels decreases the higher the sea level rise scenario. Accordingly, the conclusion is that it is imperative to consider morphodynamics in future hydrodynamic-numerical models. Especially in highly dynamic systems like the North Frisian Wadden Sea, this results in a significant added value for future planning tasks of coastal flood protection.